(1) Field of the Invention
The present invention relates to a device used for measuring the permittivity of insulating materials over a broad range of frequencies.
(2) Description of the Prior Art
The electrical property of an insulator is an important piece of information that gives the designer the ability to choose the most appropriate material for a given application of the numerous electric characteristics that describe a given insulator, the relative permittivity (Symbol: ∈r) receives attention because the relative permittivity describes an insulator's ability to store and/or dissipate electric field energy. This is symbolized by writing ∈r, explicitly as the complex quantity.∈r=∈r′−j∈r″  (1)
In the above, ∈r′ is called the dielectric constant and ∈r″ is the loss factor, both quantities varying with applied frequency. The symbol j indicates that there is a (90°) phase lag between ∈r″ and ∈r″. In a good dielectric, ∈r′ is much larger than ∈r″; the converse is true for a highly dissipative (lossy) insulator. Thus materials with loss factors large compared to the dielectric constant exhibit a temperature rise when exposed to intense field or high frequencies.
In certain applications, the magnetic properties of a material are required. For example: the magnetic properties of radar absorbing material (RAM). In this case, the relative permeability (Symbol μr) must be known for the absorption capability of the RAM.
The permeability of a material is also a complex quantity and is written in the same way, that is,μr=μr′−jμr″  (2)as it analogously describes the manner in which the material interacts with magnetic fields.
As described above, there exists a need for a device for measuring the permittivity and leading to a future method for measuring the permeability of either dielectric or magnetic materials or composites thereof over a wide band of frequencies. The important feature of the device is that it be nondestructive, so that the material to be tested does not require machining to any particular shape as required with other methods. Only a smooth flat surface is required for the device.